Apparatus and a record carrier for, and a method of recording a sequence of video data signals

ABSTRACT

An apparatus for recording a sequence of video data signals on a record carrier includes input structure for receiving video data signals, generating structure for generating characteristic point information signals, processing structure for processing the characteristic point information signals for a plurality of characteristic points into a sequence of characteristic points information signals (CPI) and writing structure for writing the sequence of video data signals and the sequence of characteristic points information signals on the record carrier. The characteristic point information signals identify a characteristic point in the sequence of video data signals. Various measures are proposed in relation to the CPI aiming at providing compact way of storing information related to a size of I-pictures.

The invention relates to an apparatus for recording a sequence of videodata signals on a record carrier, the sequence of video signalscomprising pictures of an intra-picture type coded without reference toother pictures and pictures of an inter-picture type coded withreference to other pictures,

the apparatus comprising:

-   -   input means for receiving video data signals;    -   generating means for generating characteristic point information        signals, the characteristic point information signals        identifying a characteristic point in the sequence of video data        signals, the characteristic point information signals comprising        a block of information, the block of information comprising:        -   position data defining a position of the characteristic            point in the sequence of video data signals; and        -   size data providing information related to a size of an            I-picture selected from the pictures of the intra-picture            type;    -   processing means for processing the characteristic point        information signals for a plurality of characteristic points        into a sequence of characteristic points information signals;        and    -   writing means for writing the sequence of video data signals and        the sequence of characteristic points information signals on the        record carrier.

The invention further relates to an apparatus for reproducing a sequenceof video data signals comprising pictures of an intra-picture type codedwithout reference to other pictures and pictures of an inter-picturetype coded with reference to other pictures, using for the sequence ofvideo data signals a corresponding sequence of characteristic pointsinformation signals comprising characteristic point information signalsfor a plurality of characteristic points, the characteristic pointinformation signals identifying a characteristic point in the sequenceof video data signals, the characteristic points information signalscomprising a block of information which comprises:

-   -   position data defining a position of the characteristic point in        the sequence of video data signals; and    -   size data providing information related to a size of an        I-picture selected from the pictures of the intra-picture type;        the apparatus comprising:    -   input means for receiving the sequence of video data signals and        the corresponding sequence of characteristic points information        signals;    -   extracting means for extracting the block of information from        the sequence of characteristic points information signals; and    -   processing means for processing the sequence of video data        signals into video data signals using the block of information.

In addition, the invention relates to a method of generating a sequenceof information signals concerning characteristic points in a sequence ofvideo data signals comprising pictures of an intra-picture type codedwithout reference to other pictures and pictures of an inter-picturetype coded with reference to other pictures, in which for acharacteristic point a block of information is generated, the block ofinformation comprising:

-   -   position data defining a position of the characteristic point in        the sequence of video data signals; and        size data providing information related to a size of an        I-picture selected from the pictures of the intra-picture type.

Furthermore, the present invention relates to a record carrier providedwith the sequence of video data signals and the sequence ofcharacteristic points information signals.

The CPI (Characteristic Point Information) table maps the time axis (themoment a certain picture or scene is shown in the program) on thelocation (byte number) in the file, which contains the bytes from theprogram. This is especially important if the bit rate is not known ornot constant. The characteristic points make it possible to have randomaccess, based on presentation time, in the recorded program. FIG. 1shows schematically location of characteristic points (CP) in the file.The axis P represents position in the file.

In FIG. 2 a schematic view is given of the layered structure of astorage device.

Files created in the AV-Application (APP) are sent to the File Systemlayer (FS). Here a mapping of the bytes from the files on the logicaladdress space which is delivered by the Bit Engine (BE) is made. Thismapping is stored in the FS database.

In the Bit Engine the mapping of the logical address space on thephysical address space is carried out. The files, which are created inthe AV-application, are: the real-time files, which contain the contentof the AV program and an AV database. The AV database contains thenavigation data for access to the real-time files. The CPI table is partof the navigation data and it is stored in the AV data base file.

Characteristic points in case of an MPEG2 coded AV signal, on the timeaxis are:

-   -   the start of a so-called I-picture (intra-picture),    -   the start of a P-picture,    -   the start of an Audio access unit (in case of an Audio only        signal).        The start of the I-picture is most important because decoding        can start without the need of previous information. The start of        a P-picture could be important if the previous I-picture (or        P-picture) is also mentioned.

During operation the CPI table of the program, which is presented, isstored in (DRAM) memory of the Application layer. That is why the sizeof the CPI table should be limited. CPI tables can be very large, as isexplained in next example.

The address from the position in the file is represented by the sourcepacket number in that file. With an MPEG2 Transport Stream, each sourcepacket consists of the Transport Stream packet of 188 bytes and a Timestamp of 4 bytes. With a capacity of 25 Gbytes we need 28 bits torepresent this address of a characteristic point in the program.

The accuracy on the time access should be less than the duration ofaccess units. With an accuracy of 5 msec and a total playing time of 24hours we need 25 bits to represent the timing information.

The CPI table from a stored program might contain a lot of entries. Theduration of a Group-Of-Pictures (GOP) is less than half a second. EachGOP starts with an I-picture. If an entry in the CPI table is made forall I-pictures, then there are for every hour playing time at least 7200entries. The playing time of a large capacity disc could be very large(e.g. 12 hours), which results in about 100.000 entries.

With 4 bytes for the address and another 4 bytes for the presentationtime we end up at a size of 800 Kbytes.

The CPI table is also used for trick play like fast forward and reverse.In trick play not all pictures can be presented. Very often only theI-pictures (I), or some of the I-pictures, are presented as shown inFIG. 3. So not all source packets have to be read but only those whichare used for presentation. The size of the I-picture is not fixed, sizecould be tens or hundreds of Kbytes.

Reading of redundant information costs time, in that time anotherI-picture could have been read. This improves the trick play performancebecause more pictures per second could have been presented.

In some other systems this is solved by having for each entry in the CPItable not only the presentation time and the address in the file butalso the size of the I-picture or the address of the source packet,which contains the last byte from the I-picture. The size of theI-picture is measured in source packets with a size of 192 bytes. Thesize of an I-picture could be several hundreds of Kbytes. More than 10bits are needed to indicate the size of the I-picture. This would resultin another 2 bytes for the entry in the table. The size of the table isincreased and it is not 4 byte aligned anymore.

In the drive only units of ECC blocks (B) can be read. If only a fewbytes are needed from a certain ECC block then still the whole ECC blockhas to be read.

It is of no use to indicate very accurately the size of the I-picture.This-is schematically shown in FIG. 4. It is enough if it is known thatonly two ECC blocks have to be read instead of 5 ECC blocks. In thefollowing paragraph some numbers are given which might occur inpractice.

Bit rate of the MPEG Transport Stream is 8 Mbps (1 Mbytes per second).

One GOP is 0.5 second, so the average size of the GOP is 0.5 Mbytes.

The size of an ECC block is 64 Kbytes, so one GOP is in average 8 ECCblocks.

The maximum size of an I-picture is taken equal to the decoding buffer(˜225 Kbytes, ˜4 ECC blocks).

The average size of the I-picture is much less, it might be in the orderof 100 Kbytes (<2 ECC blocks).

If it is indicated that the size of the I-picture is <128 Kbytes, thennever more than 3 ECC blocks have to be read. If this size was not knownthen 5 ECC blocks had to be read.

The aim of this proposal is to have an indication for the size of theI-picture. So not more ECC blocks are read than is needed. But also tokeep the number of bits for the size of the I-picture as low aspossible. For this purpose we can use following property.

If the video type indicates that it is an entry for a P-picture, thenthe size is not important. P-pictures for trick play are only importantat low speeds. Here either the end of the picture can be found whilereading and as soon as the end is found a jump is made to the start ofthe next picture, or the whole stream is read.

These considerations have led to the structure of one entry in the CPItable shown in FIG. 5. Presentation time stamp (PTS) specifies a timeduring presentation of the sequence of video data when a particularpicture is to be presented and a source packet number (SPN) specifies anaddress in the sequence of video data where the characteristic point islocated. TYP contains information related to a type of the entry and asize of the I-picture. In this example the entry in the CPI table has asize of 4 bytes: 4bits for TYP, 11-bits for PTS and 17-bits for SPN.

In the 4 bits from TYP, the type of the video entry is presentedtogether with the size of the I-picture. The type of the entry is givenby bits b0 . . . b3:

-   1xxx I-picture with sequence header, xxx represents the size of the    picture.-   0yyy I-picture without sequence header, yyy represents the size of    the I-picture.    At least one of the bits in yyy is ‘1’-   0000 P-picture

Examples of values for xxx and yyy are given in Table 1, where k is thescaling factor.

Size of I- xxx yyy picture 000 000 not relevant 001 001 <k*s1 010 010k*s1 . . . k*s2 011 011 k*s2 . . . k*s3 100 100 k*s3 . . . k*s4 101 101k*s4 . . . k*s5 110 110 k*s5 . . . k*s6 111 111 >k*s6

As an example:

For standard definition TV (SD-TV): k=1

For high definition TV (HD-TV): k=2

and s1=64 kB

s2=128 kB

s3=192 kB

s4=256 kB

s5=320 kB

s6=384 kB

In another example k-1 and: s1=128 kB, s2=256 kB, s3=384 kB, s4=576 kB,s5=896 kB, s6=1280 kB.

In yet another example TYP can have length of 3-bits with only 1-bitcarrying information related to the I-picture size. Its value can bebinary ‘1’ for I-pictures with size smaller than 128 kB and binary ‘0’for cases when the size is not specified.

FIG. 1 shows schematically location of characteristic points (CP) in thefile.

FIG. 2 shows a schematic view of the layered structure of a storagedevice.

FIG. 3 shows schematically location of I-pictures (I) in the file.

FIG. 4 shows schematically I-pictures (I) and ECC blocks (B).

FIG. 5 shows example of one entry in the CPI table.

FIG. 6 shows an embodiment of the apparatus for recording a sequence ofvideo data signals, in accordance with the invention.

FIG. 6 shows an embodiment of the apparatus for recording a sequence ofvideo data signals, in accordance with the invention. The apparatuscomprises an input terminal 1 for receiving video data signals and avideo data signals processing unit 100. The signals processing unit 100receives the video data signals via the input terminal 1 and processesthe video data signals into a sequence of video data signals forrecording the sequence of video data signals on a record carrier 3.Further, a read/write unit 102 is available. The read/write unit 102comprises a read/write head 104, which is in the present example anoptical read/write head for reading/writing the sequence of video datasignals and a corresponding CPI from/on the record carrier 3. Further,positioning means 106 are present for positioning the head 104 in aradial direction across the record carrier 3. A read/write amplifier 108is present in order to amplify the signal to be recorded and amplifyingthe signal read from the record carrier 3. A motor 110 is available forrotating the record carrier 3 in response to a motor control signalsupplied by a motor control signal generator unit 112. A microprocessor114 is present for controlling all the circuits via control lines 116,118 and 120.

The signals processing unit 100 is further adapted to generate thecorresponding CPI for the sequence of video data signals. To thatpurpose, the signals processing unit 100 is, as an example, capable ofidentifying position and size of an I-picture in the sequence of videodata signals. Further, the signals processing unit 100 is capable ofgenerating a block of information for a characteristic pointcorresponding to this I-picture, consisting of TYP, PTS and SPN asdefined in above examples.

The CPI can be temporarily stored in a memory 132, until the processingof the video data signals into the sequence of video data signals and,eventually, the subsequent recording on the record carrier 3, has beencompleted. Next, the CPI stored in the memory 132 can be recorded on therecord carrier 3.

1. An apparatus for recording a sequence of video data signals on arecord carrier, the sequence of video signals comprising pictures of anintra-picture type coded without reference to other pictures andpictures of an inter-picture type coded with reference to otherpictures, the apparatus comprising: input means for receiving video datasignals; generating means for generating characteristic pointinformation signals, the characteristic point information signalsidentifying a characteristic point in the sequence of video datasignals, the characteristic point information signals comprising a blockof information, the block of information comprising: position datadefining a position of the characteristic point in the sequence of videodata signals; and size data providing information related to a size ofan I-picture selected from the pictures of the intra-picture type;processing means for processing the characteristic point informationsignals for a plurality of characteristic points into a sequence ofcharacteristic points information signals; and writing means for writingthe sequence of video data signals and the sequence of characteristicpoints information signals on the record carrier; characterized in thatthe apparatus comprises: classifying means for classifying the size ofthe I-picture in a size interval out of a plurality of predefined sizeintervals; mapping means for mapping the size interval into the sizedata.
 2. An apparatus as claimed in claim 1, characterized in that theclassifying means are designed to classify the size of the I-pictureaccording to a distribution of the size of the pictures of theintra-picture type.
 3. An apparatus as claimed in claim 1, characterizedin that the mapping means are designed to use one bit for the size data.4. An apparatus as claimed in claim 1, characterized in that theclassifying means are designed to use size intervals of differentlengths.
 5. An apparatus as claimed in claim 1, characterized in thatthe classifying means are designed to use the size intervals which arequantized in multiplies of a size of an error correction code cluster.6. An apparatus as claimed in claim 1, wherein the block of informationcomprises an identification data identifying a type of a pictureselected from the pictures of the intra-picture type and the pictures ofthe inter-picture type, the apparatus characterized in that thegenerating means are designed to combine the identification data withthe size data.
 7. An apparatus as claimed in claim 1, the record carrierbeing a disc-like optical record carrier, characterized in that thewriting means comprise an optical read/write head, a positioning meansfor positioning the optical read/write head and moving means forrotating the record carrier.
 8. An apparatus for reproducing a sequenceof video data signals comprising pictures of an intra-picture type codedwithout reference to other pictures and pictures of an inter-picturetype coded with reference to other pictures, using for the sequence ofvideo data signals a corresponding sequence of characteristic pointsinformation signals comprising characteristic point information signalsfor a plurality of characteristic points, the characteristic pointinformation signals identifying a characteristic point in the sequenceof video data signals, the characteristic points information signalscomprising a block of information which comprises: position datadefining a position of the characteristic point in the sequence of videodata signals; and size data providing information related to a size ofan I-picture selected from the pictures of the intra-picture type; theapparatus comprising: input means for receiving the sequence of videodata signals and the corresponding sequence of characteristic pointsinformation signals; extracting means for extracting the block ofinformation from the sequence of characteristic points informationsignals; and processing means for processing the sequence of video datasignals into video data signals using the block of information;characterized in that: the extracting means are designed to retrieve thesize data and to map the size data into a size interval out of aplurality of predefined size intervals; the processing means aredesigned to use information related to the size interval.
 9. Anapparatus as claimed in claim 8, wherein the block of informationcomprises an identification data identifying a type of a pictureselected from the intra-pictures and the inter-pictures, the apparatuscharacterized in that the means for extracting the block of informationare designed to separate the identification data from the size data. 10.An apparatus as claimed in claim 8, characterized in that the inputmeans are designed to receive the sequence of video data signals and thecorresponding sequence of characteristic points information signals froma record carrier.
 11. An apparatus as claimed in claim 10, characterizedin that the input means are designed to receive the sequence of videodata signals and the corresponding sequence of characteristic pointsinformation signals from a disc-like optical record carrier.
 12. Amethod of generating a sequence of information signals concerningcharacteristic points in a sequence of video data signals comprisingpictures of an intra-picture type coded without reference to otherpictures and pictures of an inter-picture type coded with reference toother pictures, in which for a characteristic point a block ofinformation is generated, the block of information comprising: positiondata defining a position of the characteristic point in the sequence ofvideo data signals; and size data providing information related to asize of an I-picture selected from the pictures of the intra-picturetype; characterized in that, the size of the I-picture is classified ina size interval out of a plurality of predefined size intervals; and thesize interval is mapped into the size data.
 13. A method as claimed inclaim 12, characterized in that the size of the I-picture is classifiedin the size interval according to a distribution of sizes of thepictures of the intra-picture type.
 14. A method as claimed in claim 12,characterized in that one bit in the block of information is used forthe size data.
 15. A method as claimed in claim 12, characterized inthat the size intervals have different lengths.
 16. A method as claimedin claim 12, characterized in that the size intervals are quantized inmultiplies of a size of an error correction code cluster.
 17. A methodas claimed in claim 12, wherein the block of information comprises anidentification data identifying a type of a picture selected from thepictures of the intra-picture type and the pictures of the inter-picturetype, characterized in that the identification data is combined with thesize data.